This request is for funds to purchase a Leica Stimulated Emission Depletion (STED) 3X microscope with 3 depletion lines. This instrument will be housed within the Center for Biologic Imaging (CBI) at the University of Pittsburgh School of Medicine. The mandate of this core facility is to provide access to a full range of light and electron optical, image analysis, and morphometric methods to all research groups within the University of Pittsburgh School of Medicine. Super-resolution microscopy is an essential service provided by the center. Until last year the improvement in resolution using STED, while significant was limited in commercial systems to improvements in the XY axis with no improvements in Z resolution. However, with the release of a STED solution that is effective in all 3 axis the approach has become much more useful. Furthermore when equipped with 3 depletion lines the method works with many conventional fluorophores allowing facile 3 color super-resolution imaging such that it can be easily deployed in a core environment such as the CBI. The need for this instrument is demonstrated in this application with several diverse NIH supported projects in fields including; Neurobiology, Cell Biology, Developmental Biology, Infectious Disease, cytoskeletal biology, and basic Mitochondrial function. Since the CBI commenced operations 24 years ago, it has become an integral part of the medical research community currently participating in research projects with more than 300 PHS funded groups within the medical area, as well as in PHS supported projects with investigators in other departments and at neighboring institutions. The steering committee of the CBI feel that acquisition of a 3X STED system as an essential addition to the repertoire of instrumentation available to PHS funded users of the Center.